Messages in this thread Patch in this message | | | From | Ming Lei <> | Subject | [PATCH 1/2] blk-mq: fix race between timeout and queue_rq | Date | Wed, 17 Sep 2014 17:47:57 +0800 |
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Either the request is from requeue or just being allocated from tag pool, its REQ_ATOM_STARTED flag has been cleared already, so don't test it in blk_mq_start_request().
One memory barrier is needed between writing rq->deadline and setting REQ_ATOM_STARTED so that timeout can't happen too early if timeout handler reads obsolete rq->deadline caused by out of order of the two writes.
Signed-off-by: Ming Lei <ming.lei@canonical.com> --- block/blk-mq.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/block/blk-mq.c b/block/blk-mq.c index 47f3938..957815e 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -377,13 +377,20 @@ static void blk_mq_start_request(struct request *rq, bool last) blk_add_timer(rq); /* + * Order writing rq->deadline and setting the rq's + * REQ_ATOM_STARTED flag so that timeout handler can see + * correct rq->deadline once the rq's REQ_ATOM_STARTED flag + * is observed. + */ + smp_mb__before_atomic(); + + /* * Mark us as started and clear complete. Complete might have been * set if requeue raced with timeout, which then marked it as * complete. So be sure to clear complete again when we start * the request, otherwise we'll ignore the completion event. */ - if (!test_bit(REQ_ATOM_STARTED, &rq->atomic_flags)) - set_bit(REQ_ATOM_STARTED, &rq->atomic_flags); + set_bit(REQ_ATOM_STARTED, &rq->atomic_flags); if (test_bit(REQ_ATOM_COMPLETE, &rq->atomic_flags)) clear_bit(REQ_ATOM_COMPLETE, &rq->atomic_flags); -- 1.7.9.5
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